Systemd offical list of services?

good day all
i'v been looking on google for an official list of SERVICES flies with definitions .
there seems there are no man pages either .
shouldn't there be a official list some where ?

Is this what you want?

no not quite , definitions.

accounts-daemon.service 

is a potential security risk. It is part of AccountsService, which allows programs to get and manipulate user account information. I can't think of a good reason to allow this kind of behind-my-back operations, so I mask it.

avahi-daemon.service

is supposed to provide zero-configuration network discovery, and make it super-easy to find printers and other hosts on your network. I always disable it and don't miss it.

this was taken from a blog written by some one else , shouldn't there be something official explaining what each does ?

Services are run by various programs; so you won't be find anything "official" in a single place. For example the accounts service is a DBUS service; so you have try finding your necessary details in freedesktop.org.